In a tweet, the president offered “sympathy and best wishes” to loved ones of the 49 reported dead and the dozens injured so far in two mosque attacks that took place early Friday morning, while offering U.S. assistance to New Zealand's government.

“My warmest sympathy and best wishes goes out to the people of New Zealand after the horrible massacre in the Mosques. 49 innocent people have so senselessly died, with so many more seriously injured. The U.S. stands by New Zealand for anything we can do. God bless all!” the president tweeted.

My warmest sympathy and best wishes goes out to the people of New Zealand after the horrible massacre in the Mosques. 49 innocent people have so senselessly died, with so many more seriously injured. The U.S. stands by New Zealand for anything we can do. God bless all!

A statement by White House press secretary Sarah Huckabee Sanders echoed the president, calling the attack a “vicious act of hate.”

“The United States strongly condemns the attack in Christchurch. Our thoughts and prayers are with the victims and their families. We stand in solidarity with the people of New Zealand and their government against this vicious act of hate," Sanders said, according to pool reports.

Other world leaders were quick to condemn Friday's massacre as well.

London Mayor Sadiq Khan, a practicing Muslim who was reportedly mentioned in the shooter's manifesto, added that patrols in London around local mosques would be increased.

"When the flames of hatred are fanned, when people are demonised because of their faith, when we play on people's fears rather than addressing them, the consequences are deadly, as we have seen so sadly today," Khan tweeted.

"In response to the horrific attack in New Zealand, I am in constant contact with @metpoliceuk who are stepping up reassurance patrols around mosques & increasing engagement with communities of all faiths," he continued.

In response to the horrific attack in New Zealand, I am in constant contact with @metpoliceuk who are stepping up reassurance patrols around mosques & increasing engagement with communities of all faiths.

Friday's attack occurred at two mosques in the New Zealand city, according to authorities, who reported that four people were detained, including one Australian, following the shooting.

Officials said they detained a 28-year-old man identifying himself as the shooter who posted a manifesto online as well as photos and videos of the shooting. The suspect declared himself to be a 28-year-old Australian radicalized online by right-wing influences.

New Zealand's Prime Minister Jacinda Ardern called the violence an act of terrorism.

"It is clear that this can now only be described as a terrorist attack,” Ardern said.

"What has happened in Christchurch is an extraordinary act of unprecedented violence. It has no place in New Zealand. Many of those affected will be members of our migrant communities — New Zealand is their home — they are us," she continued on Twitter.